The present invention relates to a device for a goniometric examination of the optical properties of surfaces. The device will be described below with reference to examining car bodywork. However, reference is made to the fact that the device of the invention may also be applied to examining other kinds of surfaces.
Such devices for a goniometric examination of the optical properties of surfaces are known from the prior art. Generally, these use a light source which emits light to the surface to be examined and a detector that detects and evaluates the light reflected or diffused off said surface. Such evaluation allows a determination of the optical properties of surfaces such as color or gloss. Such determination or characterization is required since motor-vehicle bodies or their paintwork make different impressions on the human eye depending on the incident light, thus requiring a neutral characterization.
Lately finishes have been gaining popularity which comprise in particular pigments or so-called flakes. These pigments or flakes are for instance metal particles statistically distributed in the layer of finish or its surface. More precisely, metal pigments may consist of very thin metal flakes acting as miniature reflectors. Standardizing these types of finishes or measuring the properties of their surfaces creates problems since, depending on the incidence angle of the light, said pigments exhibit different characteristics and for example the slightest variation of the viewing angle may already result in a different color or a different brightness.
Among other things manufacturers also use finishes having interference pigments which, in particular in viewing large surface areas, result in color blending at more or less precisely specified color alteration angles (Flop) which may lead to largely different color perceptions which in turn leads to varying overall impressions of the brightness or color of the finished surfaces.
These effects and different perceptions of surfaces caused for example by different densities, distribution and compositions of finish additives such as flakes or ornamental pigments cannot be detected with prior art devices since those detectors only supply information on the composite intensity of the incident light from various positions on the measuring surface i.e. they integrate intensity without local resolution.